I have been working on this project where the client wanted to be able to upload and install image galleries, so I have worked with this one and I love it: mhttp://alexrabe.de/wordpress-plugins/nextgen-gallery/

All was smooth and working until, I removed this one line of code from my header.php in my WordPress theme directory.

<?php wp_head() ?>

Without this function in your header.php the gallery does not know where to insert the CSS/JavaScript files to create a fully functioned gallery. Be sure that it is placed before your closing tag.

To find out more information on the function check out this

All in all, be sure if you are running any type of plugin where they need to insert code upon plugin creation that you have that line within your head element of the page.

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